The present invention relates an automotive air conditioning apparatus with an electrical compressor used for air conditioning.
Recent automotive air conditioning systems use an electrical compressor which is controlled to provide air conditioning inside the vehicle with no relationship to the engine speed. An automotive air conditioning system of this type as described in Japanese patent S63-57316 is described below with reference to FIGS. 1 and 2.
This system is installed in a bus 21 with a rear-mounted drive engine 22. A generator 23 is connected to the drive shaft of the engine 22 by means of an electromagnetic clutch 24. The air conditioning unit 25 comprises the components required by the cooling cycle. The electrical power needed by the air conditioning unit 25 is provided by the generator 23 and conducted over electrical lines 26.
Conditioned air from the air conditioning unit 25 is supplied to the bus interior through ducts 27 mounted on the ceiling of the bus 21. The air conditioning unit 25 comprises an inverter 28 which receives the electricity produced by the generator 23. The compressor 29 produces the cooling cycle, and features a sealed structure with a built-in sealed drive motor.
The other components of the air conditioning unit 25 include the external air heat exchanger 30, internal air heat exchanger 31, a cooling fan 32 and 33 for each of the heat exchangers, respectively, and an expansion means 34 provided in the cooling cycle between the external air heat exchanger 30 and internal air heat exchanger 31. The compressor 29 and fans 32 and 33 are driven by the electricity produced by the generator 23 and frequency adjusted by the inverter 28.
The control panel 35 that controls the inverter 28 and the electromagnetic clutch 24 is connected to these components by electrical wires 36 and 37.
The driver can thus operate the control panel 35 to control the air conditioning system whenever the engine 22 is running, and the control commands from the control panel 35 are relayed over electrical wires 36 and 37 to operate the electromagnetic clutch 24 and inverter 28.
When the electromagnetic clutch 24 is engaged, the generator 23 is driven by the engine 22 to produce electricity. Because the electrical power frequency changes with the engine 22 speed, the electrical power produced by the generator 23 is supplied to the inverter 28 to be converted to the appropriate frequency.
This frequency adjusted electrical power is then used to drive the compressor 29 and fans 32 and 33. The coolant is thus circulated by the compressor 29 through the external air heat exchanger 30, expansion means 34, and internal air heat exchanger 31, and the bus interior is air conditioned by the operation of the internal air heat exchanger 31.
As thus described, there are existing systems which have an integral generator to drive a compressor, and control the compressor speed independently of the engine speed to air condition the interior of the vehicle.
In addition, when the temperature inside the vehicle is high, the compressor is operated at a higher speed, and when the temperature inside the vehicle drops, the compressor speed is again lowered.
Unfortunately, however, the generating capacity of the generator supplying the electrical power needed to drive the compressor is dependent upon the engine speed. The air conditioning system controlled as described in Japanese patent S63-57316 therefore requires a physically large generator to assure sufficient generating capacity when the engine speed is low, and this limitation restricts the practical applicability of this air conditioning system. In addition, when the generator in this system is used to provide electrical power for both the air conditioning system and other electrical equipment, the generator output becomes saturated and the output voltage drops sharply, resulting in an adverse affect on the connected electrical equipment, when the heat load inside the vehicle is high, the electrical consumption of the other equipment is high, and the total-electrical consumption exceeds the output capacity of the generator.